Various types of bone anchors are used to engage implants and other types of devices to bone. In the spinal field, bone screws are commonly used to attach plates, rods and other types of implants and devices to one or more vertebrae. Many existing bone screws include a threaded shank portion adapted for engagement in bone, and a head portion for coupling to an elongate member such as a spinal rod.
Breakage of bone screws in orthopedic applications is a somewhat common adverse event which may be caused, for example, by trauma, obesity, dynamic movement, non-unions or other events or actions that lead to screw fatigue failure. Bone screw breakage typically occurs below the head portion of the bone screw and adjacent the surface of the bone where the threaded shank portion has penetrated into the bone. Since the head portion of the bone screw normally includes the structural features that serve to drive the screw into bone, the process of extracting the threaded shank portion from the bone after the head portion has broken away from the remainder of the screw can be difficult and time consuming, and may require removal of a portion of the bone material adjacent the threaded shank portion which can lead to weakening of the structure of the bone.
Thus, there remains a need for an improved bone anchor having a predetermined break point and/or removal features. The present invention satisfies this need and provides other benefits and advantages in a novel and unobvious manner.